Cancer
Cancer is one of the most common diseases, and a major cause of death in the western world. In general, incidence rates increase with age for most forms of cancer. As human populations continue to live longer, due to an increase of the general health status, cancer may affect an increasing number of individuals. The cause of most common cancer types is still largely unknown, although there is an increasing body of knowledge providing a link between environmental factors (dietary, tobacco smoke, UV radiation etc) as well as genetic factors (germ line mutations in “cancer genes” such as p53, APC, BRCA1, XP etc) and the risk for development of cancer.
No definition of cancer is entirely satisfactory from a cell biological point of view, despite the fact that cancer is essentially a cellular disease and defined as a transformed cell population with net cell growth and anti-social behavior. Malignant transformation represents the transition to a malignant phenotype based on irreversible genetic alterations. Although this has not been formally proven, malignant transformation is believed to take place in one cell, from which a subsequently developed tumor originates (the “clonality of cancer” dogma). Carcinogenesis is the process by which cancer is generated and is generally accepted to include multiple events that ultimately lead to growth of a malignant tumor. This multi-step process includes several rate-limiting steps, such as addition of mutations and possibly also epigenetic events, leading to formation of cancer following stages of precancerous proliferation. The stepwise changes involve accumulation of errors (mutations) in vital regulatory pathways that determine cell division, asocial behavior and cell death. Each of these changes may provide a selective Darwinian growth advantage compared to surrounding cells, resulting in a net growth of the tumor cell population. A malignant tumor does not only necessarily consist of the transformed tumor cells themselves but also surrounding normal cells which act as a supportive stroma. This recruited cancer stroma consists of connective tissue, blood vessels and various other normal cells, e.g., inflammatory cells, which act in concert to supply the transformed tumor cells with signals necessary for continued tumor growth.
The most common forms of cancer arise in somatic cells and are predominantly of epithelial origin, e.g., prostate, breast, colon, urothelium and skin, followed by cancers originating from the hematopoetic lineage, e.g., leukemia and lymphoma, neuroectoderm, e.g., malignant gliomas, and soft tissue tumors, e.g., sarcomas.
Cancer Diagnostics and Prognostics
Microscopic evaluation of biopsy material from suspected tumors remains the golden standard for cancer diagnostics. To obtain a firm diagnosis, the tumor tissue is fixated in formalin, histo-processed and paraffin embedded. From the resulting paraffin block, tissue sections can be produced and stained using both histochemical, i.e., hematoxylin-eosin staining, and immunohistochemical (IHC) methods. The surgical specimen is then evaluated with pathology techniques, including gross and microscopic analysis. This analysis often forms the basis for assigning a specific diagnosis, i.e., classifying the tumor type and grading the degree of malignancy, of a tumor.
Malignant tumors can be categorized into several stages according to classification schemes specific for each cancer type. The most common classification system for solid tumors is the tumor-node-metastasis (TNM) staging system. The T stage describes the local extent of the primary tumor, i.e., how far the tumor has invaded and imposed growth into surrounding tissues, whereas the N stage and M stage describe how the tumor has developed metastases, with the N stage describing spread of tumor to lymph nodes and the M stage describing growth of tumor in other distant organs. Early stages include: T0-1, N0, M0, representing localized tumors with negative lymph nodes. More advanced stages include: T2-4, N0, M0, localized tumors with more widespread growth and T1-4, N1-3, M0, tumors that have metastasized to lymph nodes and T1-4, N1-3, M1, tumors with a metastasis detected in a distant organ. Staging of tumors is often based on several forms of examination, including surgical, radiological and histopathological analyses. In addition to staging, for most tumor types there is also a classification system to grade the level of malignancy. The grading systems rely on morphological assessment of a tumor tissue sample and are based on the microscopic features found in a given tumor. These grading systems may be based on the degree of differentiation, proliferation and atypical appearance of the tumor cells. Examples of generally employed grading systems include Gleason grading for prostatic carcinomas and the Nottingham Histological Grade (NHG) grading for breast carcinomas.
Accurate staging and grading is crucial for a correct diagnosis and may provide an instrument to predict a prognosis. The diagnostic and prognostic information for a specific tumor subsequently determines an adequate therapeutic strategy for a given cancer patient. A commonly used method, in addition to histochemical staining of tissue sections, to obtain more information regarding a tumor is immunohistochemical staining. IHC allows for the detection of protein expression patterns in tissues and cells using specific antibodies. The use of IHC in clinical diagnostics allows for the detection of immunoreactivity in different cell populations, in addition to the information regarding tissue architecture and cellular morphology that is assessed from the histochemically stained tumor tissue section. IHC can be involved in supporting the accurate diagnosis, including staging and grading, of a primary tumor as well as in the diagnostics of metastases of unknown origin. The most commonly used antibodies in clinical practice today include antibodies against cell type “specific” proteins, e.g., PSA (prostate), MelanA (melanocytes) and Thyroglobulin (thyroid gland), and antibodies recognizing intermediate filaments (epithelial, mesenchymal, glial), cluster of differentiation (CD) antigens (hematopoetic, sub-classification of lympoid cells) and markers of malignant potential, e.g., Ki67 (proliferation), p53 (commonly mutated tumor suppressor gene) and HER-2 (growth factor receptor).
Aside from IHC, the use of in situ hybridization for detecting gene amplification and gene sequencing for mutation analysis are evolving technologies within cancer diagnostics. In addition, global analysis of transcripts, proteins or metabolites adds relevant information. However, most of these analyses still represent basic research and have yet to be evaluated and standardized for the use in clinical medicine.
Platinum-Based Treatment
Platinum-based chemotherapy is used in treatment of cancers such as testicular, ovarian, cervical, lung, bladder, colorectal and head and neck cancer. Currently, there are three FDA-approved platinum-based compounds (cisplatin, carboplatin and oxaliplatin), but there are new derivatives being developed, or undergoing clinical trials (such as satraplatin and picoplatin). One goal in developing new platinum-based compounds is to minimize toxicity, which can be severe with the currently used compounds. Common side effects include kidney toxicity, nerve toxicity and loss of hearing.
Platinum Resistance
Platinum-based chemotherapeutic agents bind to DNA, thereby inducing DNA adducts, leading to cross-links that disrupt DNA structure. Usually, these damages ultimately lead to apoptosis. There is however a problem with drug resistance. A subset of tumours do not respond to conventional therapy, and this resistance could be either intrinsic or acquired.
The mechanism behind platinum resistance has not been fully elucidated, but two main pathways have been suggested: Either a failure of the platinum compound to reach target DNA, or a failure of the platinum compound to induce apoptosis after DNA adduct formation.
Failure of the platinum compound to reach tumor DNA could be due to the effect of certain proteins associated with multidrug resistance. There can also be other efflux proteins involved, for example those mediating copper transport.
A failure of the platinum compound to induce apoptosis is probably due to differences in DNA-repair systems. There are a number of mechanisms involved in DNA-repair, and particularly two of these have been associated with platinum resistance, Nucleotide excision repair (NER) and Mismtch repair (MMR).
With testicular cancer as a model system (these tumours are extremely sensitive to platinum-based chemotherapy), it has been shown that certain testicular carcinoma cell lines have a NER deficiency, in particular, low levels of excision repair cross-complementation group 1 (ERCC1) protein. In ovarian cancer cell lines it has been shown that cell lines developing cisplatin resistance had an increased ERCC1 expression.
There are indications that the MMR pathway needs to be functional in order for damages created by cisplatin and carboplatin to be detected by the cell. These compounds interfere with MMR activity, thus preventing damage repair, ultimately leading to apoptosis. If MMR is deficient, the cell can continue to proliferate with the DNA damage still present and will thereby be resistant. However, there seems to be a difference in MMR mediated resistance between different compounds; oxaliplatin may have effect in cells that are resistant to cisplatin and carboplatin.
Endpoint Analysis
Endpoint analysis for trials with adjuvant treatments for cancer gives important information on how the patients respond to a certain therapy. Overall survival (OS) has long been considered the standard primary endpoint. OS takes in to account time to death, irrespective of cause, e.g. if the death is due to cancer or not. Loss to follow-up is censored and regional recurrence, distant metastases, second primary ovarian cancers and second other primary cancers are ignored.
Today, an increasing number of effective treatments available for many types of cancer have resulted in the need for surrogate endpoints to allow for a better evaluation of the effect of adjuvant treatments. Partly due to the long follow-up period required to demonstrate that adjuvant treatments improve OS, the endpoint is often complemented with other clinical endpoints that give an earlier indication on how successful the treatment is.
In the present disclosure, the inventors show that the level of expression of a particular protein (the proposed biomarker) significantly correlates with prognosis. For this observation, two surrogate endpoints were used, namely ovarian cancer-specific survival (OCSS) and recurrence free survival (RFS). Analysis of OCSS includes time to death caused by ovarian cancer due to the original tumor. RFS includes time to any event related to the same cancer, i.e., all cancer recurrences and deaths from the same cancer are events. Distant, local and regional metastases as well as ovarian cancer specific death are considered. On the other hand, second primary same cancers and other primary cancers are ignored. Deaths from other cancers, non-cancer-related deaths, treatment-related deaths, and loss to follow-up are censored observations.